U.S. Pat. No. 3,689,734, issued to Burley et al. on Sept. 5, 1972 teaches a control system for automatic welding in which an operator can select one of several welding programs with a selector switch. The selector switch connects into circuit one of several program cards, each of which can have potentiometers and other circuitry for controlling the value of one or more welding parameters. But Burley does not teach a system in which the welding program is inaccessible to the machine operator. U.S. Pat. No. 3,567,902, issued to Stearns et al. on Mar. 2, 1971 similarly teaches a system in which a welding program can be defined on a printed circuit card which is inserted into the unit to operate according to the chosen welding program. But again, the operator participates in inserting program cards into the unit, and has controls for adjusting other welding parameters. Other patents which may have some pertinence are U.S. Pat. No. 2,529,111, issued to Steinberger on Nov. 7, 1950; U.S. Pat. No. 2,951,972, issued to Pomazal on Sept. 6, 1960; and British Pat. No. 661,671, issued to Ford Motor Co. on Nov. 28, 1951.
In electric arc welding the proper welding parameters, such as welding voltage and amperage, must be tailored for a given application. Welders typically are more concerned with welding speed, which depends primarily on wire feed rate, than with welding quality, which depends on selection of a particular welding schedule of amperage, voltage and other parameters not necessarily related to welding speed. Prior art welding controls have allowed the welder himself to vary the welding voltage, wire feed rate, and other parameters from the appropriate values for the job at hand. Welding quality has sometimes suffered as a result.
While the welder should not have unbridled discretion to change recommended settings for welding parameters as he sees fit, the welding unit should have several welding programs, allowing the operator to do several different types of jobs with one unit and without constant supervision. And finally, the programmable welding unit should include override means to allow occasional external control of the welding parameters.